The first purpose of this study is to evaluate the usefulness and effectiveness of non-invasive O2-saturation instruments as a clinical monitor in the neonatal and pediatric intensive care environments for assessing continously and in a timely manner arterial oxygenation. The second purpose of this study is to evaluate the accuracy and precision of non-invasive 02-saturation instruments in non-invasive measuring arterial hemoglobin oxygen saturation in the neonate, infant, and child.